In marking systems such as Xerography or other electrostatographic processes, a uniform electrostatic charge is placed upon a photoreceptor surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original. The latent image is developed by depositing finely divided and charged particles of toner upon the photoreceptor surface. The toner may be in dry powder form or suspended in a liquid carrier. The charged toner being electrostatically attached to the latent electrostatic image areas creates a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to a final support material, such as paper, and the toner image is fixed thereto to form a permanent record corresponding to the original.
In these electrostatic marking systems, a photoreceptor surface is generally arranged to move in an endless path through the various processing stations of the Xerographic process. Sometimes the photoreceptor is in the form of an endless belt and in other systems in the form of a drum. Since the photoreceptor surface is reusable when the toner image is transferred to a final support material such as paper, the surface of the photoreceptor is cleaned and prepared to be used once again in the copying process. In this endless path, several Xerographic related stations are traversed by the photoconductive belt or drum.
In these type systems, in one embodiment, after the transfer station, a photoconductor cleaning station is next. This cleaning station may comprise a first cleaning brush, a second cleaning brush and with the brushes is positioned a cleaning blade or doctor blade which is used to remove residual debris from the belt. A film or debris is generally caused by the toner being impacted onto the belt by the cleaning brushes. When the lubrication of this blade is below a necessary level, the blade can abrade or damage the belt. Toner is the primary lubricant used for the blade, however, a problem can exist with a degradation of the cleaning efficiency of the cleaning brushes or the blade. Without proper lubrication or other problems, this cleaning blade can tuck and seriously abrade the belt. Elastomeric cleaning blades, especially in doctor mode, run the risk of blade tucking. Blade tucking always starts at one of the working corners of the blade due to reduced blade stiffness at the corners and can work itself along the entire edge until the entire blade is flipped into a wiper mode-like position. Blade optimization for cleaning, filming, abrasion and other performance parameters is highly constrained by the blade tuck operating space. In other words, to ensure the blade is configured in such a way as to ensure some degree of tucking robustness, compromises must be made in the overall performance of the blade system.
The first brush above mentioned as used in prior art systems is responsible for nearly all of the filming on the photoconductive (PC) belt. This brush is positively charged to attract a negative charged toner and remove most of it from the PC belt. Adjacent to the first brush is a vacuum which vacuums the toner from the brush for later disposal. Any toner that may have acquired a positive charge will pass by the first positively charged brush and will be picked up by the second brush which is negatively charged. The vacuum is also adjacent to the second brush and should vacuum off the brush any residual positively charged toner. Then, as above noted, the doctor or cleaning blade scrapes off the belt any remaining toner debris or film layer. Again, after the action of the two prior cleaning brushes, there is generally not sufficient toner lubrication for an effective action by this cleaning blade. The cleaning blade will remove the film layer comprised of toner additives that is caused by the impact of the first brush against the toner and PC belt. The serious problem that has been encountered in this type of prior art arrangement is, as noted, that the cleaning blade does not get enough toner-provided lubrication and can easily tuck and scratch or damage the belt causing a relatively high replacement rate for both the belt and the cleaning blade. In addition, copy quality begins to deteriorate as the cleaning blade becomes tucked and is abraded and damaged or as the film and toner is less effectively removed from the PC belt by this blade. Another problem that results from blade tuck is increased drag imparted by the blade to the PC surface which can cause motion quality problems and degraded image quality.
Many of the prior art low volume electrophotographic printers and some high speed marking apparatus use elastic doctor blades to remove residual toner from drum or belt photoreceptors. Improvements in the reliability of such blades are desired to minimize/reduce wear-induced defects and extend the overall life of the cleaning blade. Unloaded polyurethane and other elastomeric materials are typically useful in cleaning blade materials. Improvements are required to extend the useful life of such blades and to make the doctor blades or cleaning blades more efficient.